1. Field of the Invention
The present invention relates to a backward starting locknut and more particularly to a backward starting locknut wherein the nut is applied onto a threaded rod or the like from the back or plastic insert side of the nut, yet still retains a desired amount of prevailing torque when the nut is fully threaded onto the rod. A prevailing torque is established between the nut and the rod because of a radially inwardly directed constriction provided on an inner, thick wall portion of a plastic locking insert mounted in a recess on a backside of the nut and the prevailing torque prevents unwanted turning movement and locks the nut in a selected place on the rod with a metal only front face of the nut ready for metal-to-metal contact with an arm or other member mounted on the rod.
2. Brief Description of the Prior Art
A wide variety of locknuts have been developed over the years and many of these locknuts are designed to resiliently seal around a threaded rod or other threaded element on which the nut is mounted so that a water-tight or liquid-tight joint is established between an end face of the nut and the threads of a threaded rod and/or an adjacent arm or other element carried on the rod and having a face generally normal to an end face of the nut.
There are also available "NYLON" insert nuts which are fully threaded to start the "NYLON" end first and these nuts depend on the "NYLON" insert constricting around the threads, only when clamped. These type of nuts are used for minimal load applications where a flexible and compressible joint face exists. Conventional "NYLON" insert nuts cannot be started "NYLON" end first because the "NYLON" insert is unthreaded. If, by extra force, the "NYLON" insert could be started, there is no way of making sure that the threads would be aligned during the transition to the already threaded metal nut. If a "NYLON" insert is threaded after assembly to the metal nut, it may be capable of starting "NYLON" end first but there would be no prevailing torque to provide a locking function.
The following U.S. patents disclose various types of locknuts:
Eckenback et al U.S. Pat. No. 2,399,107; Currlin U.S. Pat. No. 2,502,642; Wellman U.S. Pat. No. 2,653,641; DeHaitre U.S. Pat. No. 4,019,550; DeHaitre U.S. Pat. No. 4,126,170 and Witte et al U.S. Pat. No. 4,381,163.
Australian patent specification No. 123,346 also discloses a locking nut having a plastic insert which is compressed in an axial direction to provide a sealing or liquid-tight seal between elements.